mineral

Smoky Quartz

Smoky Quartz (SiO2 - Silicon Dioxide with trace impurities of aluminum)

Hardness: 7 (Mohs scale); Color: Brownish-grey, smoky grey, or black; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: Indistinct/Conchoidal fracture; Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Brownish-grey, smoky grey, or black
Luster: Vitreous (glassy)

Identified March 26, 2026More mineral →

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Physical properties

Formation & geological history

Formed in igneous and metamorphic rocks, particularly pegmatites and hydrothermal veins. The smoky color occurs through natural irradiation of aluminum-bearing quartz over millions of years after the crystal has formed.

Uses & applications

Commonly used in jewelry (rings, pendants), decorative ornaments, and by crystal collectors for its aesthetic and metaphysical associations. Industrial use is minimal as pure quartz is preferred for electronics.

Geological facts

The dark color is caused by free silicon formed from silicon dioxide by natural irradiation. It is the national gem of Scotland, where it is often referred to as 'Cairngorm' after the Cairngorm Mountains.

Field identification & locations

Identify by its characteristic 'smoky' translucency and glass-like luster. It will not be scratched by a steel knife. It is common in alpine-type fissures and granitic terrains worldwide, most notably in Brazil, the USA, and Switzerland.

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